Glycerol (glycerin) is a by-product of hydrocarbon ester production (biodiesel) via transesterification reaction from renewable vegetable oils and animal fats. Glycerol without further refinement is difficult to utilize as a fuel due to the potential release of acrolein when burned. In addition, if glycerol is left to settle, it may harden and cake, which may block fuel supply systems. Furthermore, impurities in the glycerol, as by-products of glycerol production, may lead to engine damage.
The increase in the production of biodiesel leads to a continued increase in the glycerol supply to the market, which may be well beyond the need for chemical byproducts. Using glycerol by-products to produce value added products, such as fuels or liquid chemicals may improve the economics of biodiesel production.
Value-added products of glycerol have been produced by pyrolysis, steam gasification and catalytic treatment. For example, hydrogen and syngas were produced from pyrolysis of glycerol with and without a carrier gas (nitrogen) in a fixed bed reactor at 400° C. to 500° C. In addition, the use of glycerol to form fuel or oil additives has been explored.
Glycerol conversions catalyzed by zeolite catalysts have also been explored. For example, the effect of the catalyst pore structure on product distribution during glycerol conversion was examined using HZSM-5, HY, HNaMOR and HZSM-22 catalysts at temperatures of 300 to 400° C. at atmospheric pressure or 2 MPa. Using the three-dimensional zeolites, HZSM-5 and HY, only oxygenates were produced at 300° C., irrespective of pressure. The oxygenates consisted of acetaldehyde, formaldehyde, propenal, acetol and relatively small amounts of heavier oxygenates. Upon increasing the temperature to 400° C., a hydrocarbon phase was formed and aromatics were identified, irrespective of the pressure.
In addition, one-dimensional medium-pore HZSM-22 catalysts have been found to be suitable for acrolein production, with 86% yield at 100% glycerol conversion. Three-dimensional medium-pore HZSM-5 results in a relatively high alkyl aromatic yield. Silica alumina produced the maximum acetaldehyde (24.5 g/100 g feed), γ-alumina produced the maximum acrolein (25 g/100 g feed) as shown in equation (1) below. Silica-alumina produced a formaldehyde yield of 9 g/100 feed and HY catalyst produced a relatively higher acetol yield of 14.7 g/100 g feed.

In the presence of aldehydes, further reaction with glycerol produces glycerol acetals, as shown in Equations (2) and (3), which may be useful as fuel additives.

Furthermore, glycerol dehydration to methyl ethers under supercritical methanol conditions without the use of catalysts has been considered. The reaction of glycerol under these conditions resulted in the formation of methyl glycerol ethers, alcohols, and diglycerol related compounds.
However, a process for producing oxygenated fuels, fuel components and additives from glycerol with relatively improved product selectivity, and which can be made continuous, remains desirable.